Variable reluctance pickup device



2 March 28, 1967 J. v. JOHNSTON 3,31

VARIABLE RELUCTANE PICKUP DEVICE Filed Feb. 17, 1965 VOLTAGE 26 O0 Ll L4 25 28 L2 EZJ 29 7 L5 0 SHAFT ANGLE 90 +O L8 L5 LOAD FIG. 2 FIG. 3

James V. Johnston,

INVENTOR. N y m, BY M J. W

W M W e M ATTORNEYS the invention, including the bridge circuit and,

United States Patent The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to an improved shaft angular position variable reluctance pickup device. A highly linear analog voltage output with respect to shaft angle is obtained with the present device.

Heretofore, it has been difiicult to obtain a linear voltage output from a transducer responding to an angular shaft position, except over a smallangle. The prior art devices are linear only within a 90 angle, or i45 from a median position. The present device provides a linear output over a 180 angle or :90 from a median shaft position.

An object of the invention is to provide a shaft position transducer which has a linear output over a wide shaft angular position.

Another object is to provide a shaft position transducer which is simple in construction and which requires a single moving part.

Yet another object is to provide a shaft position transducer which uses no slip rings or flexible leads on or for the shaft.

In essence, the invention consists of a magnetizable armature which is rotatable between a plurality of A.C. electromagnets electrically connected in a double bridge arrangement. Four U-shaped magnetic cores are disposed in a semicircle about the armature with the armature passing between the legs of each U. Each of the legs of each core carries an A.C. magnetic winding, with the windings of each core being connected on opposite sides of the bridge. Rotation of the armature causes a variation in the output between two opposite corners of the bridge.

The invention may be understood by reference to the drawings in which the same numerals are used for the same elements in the different figures and in which:

FIGURE 1 shows a perspective view of the physical arrangement of the invention,

FIGURE 2 shows a schematic diagram of the circuit of FIGURE 3 shows a graph of shaft angle vs. voltage output of the bridge.

Referring to FIGURE 1, there is shown a magnetizable ferromagnetic armature in the shape of a semicircular slab. The armature may be iron, steel or any ferromagnetiosubstance and may be either solid or laminated. Disposed about armature 10 are four U-shaped magnetic cores 11, 12, 13 and 14, each of which carries two magnetic windingsthereon, one on each leg of each U. The cores 11-14 may be stacked laminations, or solid, in case ferrites are used. Windings L4 and L8 are carried on core 11, windings L3 and L7 are carried on core 12, etc. Armature 10 is carried by a shaft and is adapted to rotate 90 clockwise or 90 counterclockwise from the median position as shown. The supports for cores 11- 14 and for shaft 15 are not shown but are obvious. The angle between the center lines of the cores is 60.

FIGURE 2 shows an A.C. source which supplies voltage to bridge 25 at points 26 and 27. Points 28 and 29 comprise the output side of bridge 25.

The windings L1-L8 are wound in such a way that at a given instant the pole containing the L1 coil is of a north polarity and the pole containing the L5 coil is of a Patented Mar. 28, 1967 south polarity. A magnetic flux will be established during this instant of time which will flow from the L1 pole face through the air gap to armature 10, through the low resistive path of the armature, then through the air gap between the armature and the pole face of the L5 coil, aroundthrough the low resistive path of the core 14 to the L1 coil. This is the same as magnetic flux paths for each of the succeeding cores around the armature. "At the same instant of time that the L1 pole face has a north polarity the L2, L3, L4 pole faces have the same polarity. Since an A.C. signal is applied to the coils, the polarity will change during the next half cycle so that coils L5, L6, L7, L8 will produce a northpolarity pole face. In examining the core 14, it can be seen that the magnetic flux pat-h impedance will change when the air gap is changed by moving the armature from between the poles L1 and L5. This change in the impedance of the flux path is reflected back into the coils generating the flux causing an apparent loss of load to the drivinggcoils. This loss of load causes the inductive reactance of the coil to change. The change of impedance in the affected coils, in turn, unbalances the bridge in FIGURE 2. As the armature continues to move, the same effect is then created in core 13 containing L2 and L6 coils. This action continues to further unbalance the bridge causing a larger voltage to appear across the bridge. As can be seen from the electrical diagram no secondary coils are needed to sense voltage unbalance. The sensing is created by the change of current flow in opposite legs of the bridge causing a current to flow through the load and balancing resistor R. The output signal contains phase and magnitude information. This signal determines the direction the armature has moved by the phase relationship of the output signal to the applied reference voltage, and the magnitude of the signal determines the angle the armature has moved through.

FIGURE 3 shows a graph of shaft angle vs. voltage output of the bridge arrangement of the invention. At its median position (as shown in FIGURE 1), a zero voltage is present between points 28 and 29. With increasing angles to the voltage increases linearly, as shown. The voltage ordinates above the angle abscissa axis are 0 phase shifted with respect to the A.C. input and those ordinates below the abscissa axis are phase displaced. Therefore, the amplitude of the voltage at 23 and 29 is an indication of the shaft angle from 0 to 90 and the phase of the voltage with respect to the input voltage is an indication of the direction through which the shaft has rotated. Beyond i90, the voltage output of the bridge becomes nonlinear with respect to the shaft angle.

The voltage output of the bridge may be used as an input to one set of deflection plates of a cathode-ray oscilloscope and theinput to the bridge may be used as the input to the other set of deflection plates. The resulting Lissajous figure(s) on the oscilloscope would be indicative of shaft angular position. Also, the bridge output and bridge input, through suitable amplification, of desired, could be used to control a selsyn motor as a repeater for the shaft angular position of the invention.

While a specific embodiment has been described, other variations on the invention may be obvious to one skilled in the art. Other uses than those specifically suggested for the invention may also be obvious, such as using the output of the invention as an input to a recording means.

While the foregoing is a description of the preferred embodiment, the following claims are intended to include those modifications and variations that are within the spirit and scope of my invention.

I claim:

1. A variable reluctance magnetic pickup including a shaft rotatable about an axis, a semicircular slab shaped armature carried by said shaft and concentric with said axis, a plurality of U-shaped magnetic cores disposed radially about said axis with the armature between the legs of each of said cores, a magnetic Winding on each of the legs of the cores, said windings being electrically connected in a bridge circuit, with opposite windings of each core being on opposite sides of said bridge.

2. A variable reluctance pickup device including a semicircular slab armature, a plurality of U-shaped magnetic cores having a magnetic winding on each leg of each core, the cores being disposed vertically with the armature being horizontal between the legs of each of the cores, the windings of the cores being electrically connected in a bridge circuit, with opposite winding of each core being connected to opposite legs of the bridge.

'3. A variable reluctance magnetic shaft angle position transducer including a semicircular disk magnetic armature concentric with the axis of the shaft, two pairs of U-shaped magnetic cores disposed radially about said axis with said armature between the legs of each of said cores and with the angles between the pairs of cores and with the angles between the cores within each pair being equal, a magnetic winding carried by each leg of each core, said windings being electrically connected in a double bridge network, wherein the two pairs of windings on a first side of said armature each have one of their ends connected to one terminal of a two-terminal A.C. source and the opposite ends of the windings of each pair of cores connected respectively to a pair of junction points, and wherein one end of each of the core windings on the opposite side of said armature are connected to the other terminal of the AC. source and the opposite ends of the windings of each pair of cores are connected respectively to the pair of junction points, the junctions comprising the output terminals of the device.

,4. The transducer in accordance with claim 3 in which the windings of each core are connected to provide attractive magnetic poles at the ends of the legs of each core and wherein all of the cores have the same magnetic polarity on one side of said armature.

No references cited.

NEIL C. READ, Primary Examiner.

T. B. HABECKER, Assistant Examiner. 

1. A VARIABLE RELUCTANCE MAGNETIC PICKUP INCLUDING A SHAFT ROTATABLE ABOUT AN AXIS, A SEMICIRCULAR SLAB SHAPED ARMATURE CARRIED BY SAID SHAFT AND CONCENTRIC WITH SAID AXIS, A PLURALITY OF U-SHAPED MAGNETIC CORES DISPOSED RADIALLY ABOUT SAID AXIS WITH THE ARMATURE BETWEEN THE LEGS OF EACH OF SAID CORES, A MAGNETIC WINDING ON EACH OF 